Train travel between venice- cinque terre and Florence

No! It is not cheaper or better to get a europass, particularly for such short, regional train trips. It is only a few euro between villages. Get your tickets for the longer legs (Venice to LaSpezia and LaSpezia to Florence) ASAP to get the best rate - if you have not already done this, you may be held to the highest rate because cheaper fares sell out. But I think it would still be better than getting a Europass. I did not actually pencil this out, but look at the cost of a 2-day pass as compared to the individual tickets. If you were to get a pass, you would not use it between CT villages, but only for the 2 longer trips.

Stick with point to point tickets. Rail passes are rarely worthwhile in Italy. All trains in Italy, except Regionale require a seat reservation. That is an additional 10 euro per leg with a pass. The advance purchase, deep discount tickets - Super Economy and Economy - make rail train pretty cheap IF you are willing to commit in advance to a fixed schedule. The discount tickets come with the usual range of limitations - no refund, one time change for economy, and no change for Super Econ. The fare for Regionale trains is fixed and never discount so do not buy those tickets on line - only at the train station. And it is very possible by this time that the discount tickets available for Aug are already so out. If that is the case, then just buy your tickets the day before or day of travel at the station. The base fare is very reasonable.

I'll take these questions:

Is the pass covering the regional train between the 5 villages in
Cinque terre?

As advised above, do not buy a pass. Buy point-to-point between Venice and La Spezia and La Spezia and Florence on Trenitalia or Captaintrain websites or when you arrive in Italy. For the Cinque Terre, there are one and two-day passes which cover use of the trails and the regionale train/buses in the region between La Spezia and Levanto. You can read about the cards here:

http://www.parconazionale5terre.it/Ecinque-terre-card.php

I didn't use to recommend these as you would have had to have used the trains a lot to break even but now that individual tickets prices have gone up (4 euro per single) it's a little better deal. You can buy them at the station in La Spezia. You must validate your pass before boarding your first train: very important.

i am planning to do the cinque terre hike.

There are many trails within the park so there's no single 'Cinque Terre hike.' Reference "Paths and Outdoor" under the "Visit the Park" dropdown:

http://www.parconazionale5terre.it/Eindex.php

If you mean the Sentiero Azzurro - or Blue Trail - that hugs the lower coast between Riomaggiore and Monterosso, be aware that two for four segments of that trail are closed so the only two you can do are between Monterosso and Vernazza, and Vernazza and Corniglia. You'll have to cover the space between Riomaggiore, Manarola and Corniglia via train, boat (Riomaggiore and Manarola only) or longer, alternate trails (reference the map on the website.)